Cryptochromes, blue-light absorbing proteins involved in the circadian clock, have been proposed to be the receptor molecules of the avian magnetic compass. In birds, several cryptochromes occur: ...Cryptochrome 2, Cryptochrome 4 and two splice products of Cryptochrome 1, Cry1a and Cry1b. With an antibody not distinguishing between the two splice products, Cryptochrome 1 had been detected in the retinal ganglion cells of garden warblers during migration. A recent study located Cry1a in the outer segments of UV/V-cones in the retina of domestic chickens and European robins, another migratory species. Here we report the presence of cryptochrome 1b (eCry1b) in retinal ganglion cells and displaced ganglion cells of European Robins, Erithacus rubecula. Immuno-histochemistry at the light microscopic and electron microscopic level showed eCry1b in the cell plasma, free in the cytosol as well as bound to membranes. This is supported by immuno-blotting. However, this applies only to robins in the migratory state. After the end of the migratory phase, the amount of eCry1b was markedly reduced and hardly detectable. In robins, the amount of eCry1b in the retinal ganglion cells varies with season: it appears to be strongly expressed only during the migratory period when the birds show nocturnal migratory restlessness. Since the avian magnetic compass does not seem to be restricted to the migratory phase, this seasonal variation makes a role of eCry1b in magnetoreception rather unlikely. Rather, it could be involved in physiological processes controlling migratory restlessness and thus enabling birds to perform their nocturnal flights.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Seed dispersal allows plants to colonise new sites and escape from pathogens and intraspecific competition, maintaining plant genetic diversity and regulating plant distribution. Conversely, most ...plant species form mutualistic associations with arbuscular mycorrhizal (AM) fungi in a symbiosis established immediately after seed germination. Because AM fungi are obligate symbionts, using the same dispersal vector as their host should be highly advantageous for their survival, but the co-dispersal of seeds and AM fungal spores has never been confirmed.
We aim to clarify the potential role of European birds, essential dispersers for many plant species, as co-dispersers of seeds and AM fungal spores.
In total, 63 bird droppings with intact seeds were placed in sterilised soil and maintained for 4 months in a protected environment to avoid contamination. Additionally, 173 bird droppings and 729 gauze swabs used to clean birds’ feet were inspected for AM fungal spores.
Although no spores were detected by direct observation of these samples, seven Rubus ulmifolius seedlings obtained from four independent droppings of Erithacus rubecula and Sylvia melanocephala were colonised by AM fungi. Our results show that birds can effectively co-disperse viable seeds and AM fungal spores, potentially over long distances, providing a pivotal mechanism to understand the cosmopolitan distribution of AM fungi.
Lay Summary Wind farm noise suppresses territorial defense behavior in a songbird. Our results show that in presence of anthropogenic noise, males responded with a much-reduced territorial defense ...signal during territorial conflict. As a result, anthropogenic noise may affect their ability to deter a rival, leading to expenditure of extra time and energy and to increased risks of injury and, as a consequence, could lead to reduced breeding success.In birds, anthropogenic noise has been linked to reduced breeding densities and success, but the mechanisms by which this occurs are currently unclear. In this study, we investigated whether wind turbine noise, an increasingly common source of anthropogenic noise in remote and rural locations, affects territory defense in a songbird, the European robin (Erithacus rubecula). We showed that robins increase low-frequency song elements in response to territorial intrusion under quiet conditions but that this response did not occur in the presence of wind turbine noise. These results are particularly interesting in light of previous work implicating low-frequency song in aggression, perhaps as a signal of body size. Thus, anthropogenic noise may affect their ability to deter an intruder, leading to expenditure of extra time and energy, to increased risks of injury and, as a consequence, reduced breeding success. Our study contributes to understanding the impact of anthropogenic noise on birds by linking disruptive noise and territorial behavior, which may be a mechanism underlying the reduction in bird breeding densities and success that has been reported in noisy areas.
Many partially migratory species show phenotypically divergent populations in terms of migratory behaviour, with climate hypothesized to be a major driver of such variability through its differential ...effects on sedentary and migratory individuals. Based on long‐term (1947–2011) bird ringing data, we analysed phenotypic differentiation of migratory behaviour among populations of the European robin Erithacus rubecula across Europe. We showed that clusters of populations sharing breeding and wintering ranges varied from partial (British Isles and Western Europe, NW cluster) to completely migratory (Scandinavia and north‐eastern Europe, NE cluster). Distance migrated by birds of the NE (but not of the NW) cluster decreased through time because of a north‐eastwards shift in the wintering grounds. Moreover, when winter temperatures in the breeding areas were cold, individuals from the NE cluster also migrated longer distances, while those of the NW cluster moved over shorter distances. Climatic conditions may therefore affect migratory behaviour of robins, although large geographical variation in response to climate seems to exist.
The disruption of daily rhythms is one of the most studied ecological consequences of light pollution. Previous work showed that several songbird species initiated dawn song earlier in areas with ...light pollution. However, the mechanisms underlying this shift are still unknown. Individuals may immediately adjust their timing of singing to the presence of artificial light (behavioural plasticity), but the observed effect may also be due to phenotype-dependent habitat choice, effects of conditions during early life or micro-evolution. The main aim of this study was to experimentally investigate how males of four common passerine species respond to day-to-day variation in the presence of artificial night lighting in terms of the timing of singing. During two consecutive breeding seasons, we manipulated the presence of light throughout the night in a cyclic fashion in several naturally undisturbed forest patches. We show that individuals of all four species immediately and reversibly adjusted their onset of dawn singing in response to artificial light. The effect was strongest in the European robin, but relatively small in the blue tit, the great tit and the blackbird. The effect in the latter two species was smaller than expected from the correlational studies. This may be coincidence (small sample size of this study), but it could also indicate that there are longer-term effects of living in light-polluted urban areas on timing of dawn singing, or that birds use compensatory behaviours such as light avoidance. We found no evidence that our light treatment had carryover effects into the subsequent dark period, but robins progressively advanced their dawn singing during the light treatment.
•Some songbirds start dawn song earlier in habitats exposed to light pollution.•This change in the timing of singing may result from behavioural plasticity.•We manipulated light at night in a cyclic fashion in undisturbed forest patches.•The study species advanced onset of dawn singing under experimental light at night.•Response was strong in the robin, but weak in blackbirds, great tits and blue tits.
The hormone melatonin, a main component of the avian circadian system, plays an important role in the physiological transitions that accompany activation of the migratory phenotype in passerine ...birds. Most small passerines migrate at night when circulating concentrations of melatonin are elevated. Previous work measured nocturnal melatonin levels of migratory birds only in captive animals, because free-living individuals are usually caught in the daytime. In this study, we compared nocturnal melatonin levels of European robins (
) caught during the day and held in cages overnight with those of birds that were caught at night and sampled immediately. We found that circulating melatonin at night was lower in birds held in cages compared with birds that were actively migrating. This result suggests that temporary caging affects the melatonin system and that, in nature, melatonin levels could be generally higher than those previously described by studies on captive birds.
Abstract
Background
Birds can act as reservoirs of tick-borne pathogens and can also disperse pathogen-containing ticks to both nearby and remote localities. The aims of this study were to estimate ...tick infestation patterns on migratory birds and the prevalence of different
Borrelia
species and tick-borne encephalitis virus (TBEV) in ticks removed from birds in south-eastern Sweden.
Methods
Ticks were collected from resident and migratory birds captured at the Ottenby Bird Observatory, Öland, Sweden, from March to November 2009. Ticks were molecularly identified to species, and morphologically to developmental stage, and the presence of
Borrelia
bacteria and TBEV was determined by quantitative real-time PCR.
Results
A total of 1339 ticks in the genera
Haemaphysalis, Hyalomma
, and
Ixodes
was recorded of which
I. ricinus
was the most abundant species. Important tick hosts were the European robin (
Erithacus rubecula
), Blackbird (
Turdus merula
), Tree pipit (
Anthus trivialis
), Eurasian wren (
Troglodytes troglodytes
)
,
Common redstart (
Phoenicurus phoenicurus
)
,
Willow warbler (
Phylloscopus trochilus
), and Common whitethroat (
Sylvia communis
).
Borrelia
bacteria were detected in 25% (285/1,124) of the detached ticks available for analysis. Seven
Borrelia
species (
B. afzelii
,
B. burgdorferi
(
s.s.
),
B. garinii
,
B. lusitaniae
,
B. turdi, B. valaisiana
, and
B. miyamotoi
) were identified.
B. turdi
was recorded for the first time in ticks in Sweden. The number of
Borrelia
cells per tick ranged from 2.0 × 10
0
to 7.0 × 10
5
.
B. miyamotoi
-containing ticks contained a significantly higher median number of
Borrelia
cells than
B. burgdorferi
(
s.l.
)-containing ticks.
B. garinii
and
B. miyamotoi
were the most prevalent
Borrelia
species in tick larvae. Larvae of
I. ricinus
with
B. garinii
were removed from seven bird species, particularly
S. communis
and
A. trivialis
, which may suggest that the larvae had contracted the
Borrelia
bacteria from or via these birds. Also, a high percentage of tick larvae containing
B. miyamotoi
was removed from
E. rubecula.
All ticks were negative for TBEV.
Conclusions
The results corroborate the view that the contributions of birds to human disease are substantial, particularly as blood hosts for ticks and for their short-, medium-, and long-distance dispersal. Moreover, several ground-foraging bird species appear to be important for the maintenance and dispersal of
Borrelia
species. The absence of TBEV in the ticks conforms to other similar studies.
Graphical Abstract
Visual (and probably also magnetic) signal processing starts at the first synapse, at which photoreceptors contact different types of bipolar cells, thereby feeding information into different ...processing channels. In the chicken retina, 15 and 22 different bipolar cell types have been identified based on serial electron microscopy and single‐cell transcriptomics, respectively. However, immunohistochemical markers for avian bipolar cells were only anecdotally described so far. Here, we systematically tested 12 antibodies for their ability to label individual bipolar cells in the bird retina and compared the eight most suitable antibodies across distantly related species, namely domestic chicken, domestic pigeon, common buzzard, and European robin, and across retinal regions. While two markers (GNB3 and EGFR) labeled specifically ON bipolar cells, most markers labeled in addition to bipolar cells also other cell types in the avian retina. Staining pattern of four markers (CD15, PKCα, PKCβ, secretagogin) was species‐specific. Two markers (calbindin and secretagogin) showed a different expression pattern in central and peripheral retina. For the chicken and European robin, we found slightly more ON bipolar cell somata in the inner nuclear layer than OFF bipolar cell somata. In contrast, OFF bipolar cells made more ribbon synapses than ON bipolar cells in the inner plexiform layer of these species. Finally, we also analyzed the photoreceptor connectivity of selected bipolar cell types in the European robin retina. In summary, we provide a catalog of bipolar cell markers for different bird species, which will greatly facilitate analyzing the retinal circuitry of birds on a larger scale.
In the vertebrate retina, bipolar cells are the only interneurons that project from the outer to the inner retina. Here, we systematically tested 12 antibodies for their ability to label individual bipolar cells in the bird retina and compared the eight most suitable antibodies across distantly related species, namely domestic chicken, domestic pigeon, common buzzard, and European robin. In addition, we also analyzed the photoreceptor connectivity of selected bipolar cell types in the European robin retina, which may not only process visual but also magnetic signals.
Magnetic compass orientation in night-migratory songbirds is embedded in the visual system and seems to be based on a light-dependent radical pair mechanism. Recent findings suggest that both ...broadband electromagnetic fields ranging from ~2 kHz to ~9 MHz and narrow-band fields at the so-called Larmor frequency for a free electron in the Earth's magnetic field can disrupt this mechanism. However, due to local magnetic fields generated by nuclear spins, effects specific to the Larmor frequency are difficult to understand considering that the primary sensory molecule should be organic and probably a protein. We therefore constructed a purpose-built laboratory and tested the orientation capabilities of European robins in an electromagnetically silent environment, under the specific influence of four different oscillating narrow-band electromagnetic fields, at the Larmor frequency, double the Larmor frequency, 1.315 MHz or 50 Hz, and in the presence of broadband electromagnetic noise covering the range from ~2 kHz to ~9 MHz. Our results indicated that the magnetic compass orientation of European robins could not be disrupted by any of the relatively strong narrow-band electromagnetic fields employed here, but that the weak broadband field very efficiently disrupted their orientation.
The magnetic compass of birds seems to be based on light-dependent radical-pair processes in the eyes. Cryptochromes are currently the only candidate proteins known in vertebrates that may serve as ...the primary radical-pair-based magnetoreceptor molecules. Previous immunohistochemical studies have suggested that cryptochrome 1a (Cry1a) is localised in the photoreceptor outer segments of the ultraviolet/violet (UV/V) cones, and it has been claimed that differences in Cry1a antibody staining intensities show that Cry1a is activated by light and that this should make Cry1a the most likely magnetoreceptive candidate molecule. Here, we present an independent study of Cry1a distribution within retinae of several bird species, ranging from non-migratory domestic chicken and rock pigeon to night-migratory passerines, using both the previously used antibody and two newly generated antibodies, one against the same epitope as the originally used antibody and one against a different epitope of Cry1a. We confirm the UV/V cone outer segment localisation of Cry1a in all the tested bird species. In some stainings, we found Cry1a immunoreactivity as a distinct punctate pattern throughout the whole length of the UV/V cone outer segments. These dots with a diameter of around 170 nm might suggest that many Cry1a molecules accumulate in distinct spots in the UV/V cone outer segments. However, we did not see any notable difference in Cry1a immunoreactivity between light- and dark-adapted retinae. We find no evidence whatsoever that a C-terminal antibody against Cry1a labels only a light-activated form of the Cry1a protein.
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